Rotary piston filling machines are well known in the art and a typical example is shown in U.S. Pat. No. 2,958,346, the subject matter of which is incorporated herein by reference thereto. Such machines are provided with a central product reservoir, the lower end of which has a plurality of radially outwardly extending ports. The reservoir and ports are adapted to be rotated about a central vertically extending axis and within a stationary cam framework. Associated with each port is a product filling station which includes a valve body having a rotatable valve disposed therein, a cylinder and piston assembly mounted thereon, and a container support. Each product station is rotated with the central hopper and its operation is controlled by the stationary cams. After a container to be filled has been loaded onto the machine, the piston is normally in its lowermost position and the rotatable valve is in its fill position. As the container and filling station are rotated with the central reservoir the piston will be moved upwardly by a cam causing a precise quantity of fluent material to be drawn within the cylinder. After the cylinder has been filled with the desired quantity of material the piston is held stationary while another cam causes the valve to rotate from a fill position to a discharge position. Next the piston is moved downwardly to discharge the fluent material within the cylinder into a container disposed below the valve body. Finally, the valve is rotated again to its fill position, and after this step has been completed the container is discharged from the filling machine.
Because of different types of materials which may be filled into containers two differing forms of rotatable valves are in common use today. The first form utilizes a rotatable valve plug formed of a non-galling nickel alloy of the type shown in U.S. Pat. No. 2,743,176 and sold under the name of Waukesha Metal. This alloy is, to date, the only existing corrosion resistant non-galling alloy which is in common use in the food industry where there is metal to metal contact with stainless steel. Rotatable valves of this alloy are utilized where the product to be filled into the container has good lubricating qualities, such as for example a vegetable oil, or products containing such oils. Valves made of Waukesha Metal are not suitable for products which have poor lubricity, such as, for example, tomato paste. Thus, it has been known in the industry to provide a second form of valve for such products. This form of valve includes a stainless steel valve plug to which a corrosion resistant inert and non-galling sleeve has been sealed on, such as for example polytetrafluoroethylene. The form of valve which has material sealed thereon has poor abrasion resistant qualities, and in addition such devices have been criticized as it is possible for the seal to open along the interface between the sleeve material and the supporting stainless steel permitting the intrusion of products which must be cleaned out in order to meet health standards. In order to fill a wide variety of products, it will be necessary to stock both rotatable valves made of Waukesha Metal as well as valves provided with a bonded sleeve. This obviously increases the cost of the machine.